1. Field of the Invention
The present invention relates to color electrophotographic methods for representing color resolving images of an original to obtain a color image, and more particularly to a color electrophotographic method and apparatus wherein a color balance of each color resolving image may be well controlled.
2. Description of the Prior Art
In order to represent color images, a conventional method is provided to obtain a color image by forming an electrostatic latent image according to a color resolving image of an original and developing it using a color developer, that is, a toner of the color cyan, magenta, yellow or black if so required.
To obtain a well color-balanced image, however, it is necessary to establish substantially the same relationship between the original image density (Do) of each image in cyan, magenta, and yellow and the print image density (Dp), as will be illustrated in FIG. 1. In the event the three curves (as shown in FIG. 2) of Do - Dp characteristics for these colors do not coincide, a copy having red lacking in yellow in the reproduced color may be obtained from a red original, a blue-green copy may be obtained from a green original, and a red-purple copy may be obtained from a purple original, and hence an image faithful to the original may not be obtained.
In the color reproduction according to the electrophotographic method, the relationship between each surface potential (V) of developer used to visualize electrostatic latent images, i.e., cyan, magenta and yellow toners, and the image density (D) are not identical. This is one of the reasons why the Do - Dp curves for the above-described colors do not coincide. In order to solve the problem noted above, efforts have heretofore been made to improve the developing characteristic of the toner with respect to the electrostatic latent image so as to approximate an ideal characteristic as shown in FIG. 1.
However, it is very difficult to completely control the developing characteristics of toner, and satisfactory results have not been obtained so far.
On the other hand, the relationship between the surface potential (V) of the electrostatic latent image on the photosensitive plate and the exposure (E) may vary according to each of the red, green, and blue filter exposures and it is difficult to make them identical. As a consequence, even if the V - D characteristics of the three toners should coincide, inconvenience may occur. That is, in the device for carrying out the color representation, due to the presence of different characteristics between color resolving filters, and of differences in wavelength sensitivity between photosensitive media, irregularity in characteristics for each device, and irregularity in characteristics of toner to be supplied, colors represented may vary. Thus, there is produced a possibility of extremely adverse effects on the color balance. In order to realize a preferable color representation, accordingly, it is necessary to experimentally control the electrostatic representation of each color resolved image and the color balance with one another according to each of the factors influencing color reproduction, but this requires skills and time. Furthermore, adjustment for variations with time would be required. Thus, it has been extremely difficult to keep excellent color reproduction possible in a better fashion with stability for a long period of time.
The present invention is proposed in view of the foregoing and to accomplish the following objects.